1. Field of the Invention
This invention relates to an oil supply structure for a chain adjuster for supporting a timing chain, with which moving portions such as crankshaft and timing chain are put for synchronizing a timing of a valve's opening and closing in an internal combustion engine used for vehicles, autocyles and outboard motors.
2. Description of the Related Art
Conventionally, a timing chain provided in an internal combustion engine of vehicle is provided with a chain adjuster for maintaining the tensile strength. As shown in FIG. 9, a timing chain 1 is put between a crankshaft 3 and a camshaft 4, and the outer circumference of the chain formed in loop is in contact with a curved-shaped pressure plate 6 as an operating part of the chain adjuster 5.
One end of the pressure plate 6 is pivoted on a cylinder block with a bolt 7, and the other end thereof contacts to a rod 10 biased by a spring 9 of a driving part block 8 of the chain adjuster 5, as a result, the pressure plate 6 is pressed against the timing chain 1.
The driving part block 8 of the chain adjuster 5 is, as shown in FIG. 10, adapted to be connected with a bolt 12 (FIG. 9) to a connection plane 11 formed on a projection from the surface of the cylinder block 2, and at the connection position (connection plane 11) a concave reservation chamber 13 is formed, from which an oil passage 14 is formed toward the deep portion of the block crosswise. And, the reservation chamber 13 and the oil passage 14 are in communication with each other through a pouring hole 15. Further, as shown in FIG. 11, since a tip end of the oil passage 14 is opened through the side surface, it is sealed with a plug 16.
The rod 10 of the thus-constructed chain adjuster 5 is extended due to the pressing force of the spring 9 of the driving part block 8, which presses the pressure plate 6 while being regulated by the pressure of the oil supplied, which, as a result, causes the tensile strength of the timing chain 1 to become appropriate (referring to Japanese Utility Model Laid-open No. Sho 57-71711). Further, oil passages provided for being in communication among an oil pump and the camshaft and valves are formed (referring to Japanese Utility Model Laid-open No. Sho 61-147312).
However, in such a construction as fastening the driving part block 8 of the chain adjuster 5 to the position of the cylinder block 2 where the reservation chamber 13 is fitted by the bolts, when forming the oil passage 14 while crossing the cylinder block 2, the oil passage 14 has to be provided in the vicinity of the surface of the cylinder block 2. Therefore, since the end portion of the oil passage 14 is opened toward the side, the opening of the passage 14 has to be sealed using a plug 16, so that the number of working processes has been increased, which causes the manufacturing cost to be increased.